Numerous methods have been developed to reduce the radiated noise levels generated by the engagement of roller chains with sprockets. One such method modulates the roller engagement by randomizing in a predetermined pattern (hereinafter "randomized") the radial seating position of the rollers engaging a sprocket while maintaining a constant chordal length between the seated rollers on the given sprocket. Such a device is disclosed in copending U.S. patent application Ser. No. 09/153,317, filed Sep. 15, 1998, assigned to the same assignee as the present application which disclosure is hereby incorporated by reference herein in its entirety.
In a sprocket of this type, the interaction between engagement positions on adjacent sprockets plays a significant role in system geometry and dynamics. If the entrance engagement of one sprocket and the exit engagement of an adjacent sprocket are both "high" or maximums, the chain strand between these two points will be shorter than normal. Conversely, if the entrance and exit engagement points are both "low" or minimums, the contained chain strand will be longer than nominal. In a tensioned system, the tensioner must be able to adequately react to these random sprocket and strand variations as well as the normal dynamics of any drive system. In systems of three or more shafts, these considerations become even more significant. These systems could conceivably be designed such that each chain strand in the system could be forced to become shorter or longer than nominal all at the same time. If this were to occur, the other components in the system would be required to react to these changes. For example, a tensioner may require additional stroke than would be normally designed to take up the additional chain slack when all strands cycle from their shortest to longest length. This change in system strand length from short to long may also occur in such a short time span that the tensioner may not respond quickly enough and loss of system control could occur. Another condition that could arise from changes in strand length is unwanted accelerations and decelerations of the driven shafts.